In and electrodynamic loudspeaker, a cone is attached to a voice coil. The voice coil is moved by an electromagnet powered by an audio amplifier. The faster and farther the cone moves, the louder the sound from the loudspeaker. In today's mobile devices, very small loudspeakers are used in order to allow for thinner and smaller devices. Smaller loudspeakers are desired for many devices in order to reduce size and to require less power to drive the loudspeakers. At the same time, mobile devices such as mobile phones and tablet computers are typically designed to reproduce acoustic signals with high loudness.
The very small loudspeakers used in mobile phones and tablets are called micro speakers. Due to their small size, their performance is limited. The total volume and contrast are both low. As a result, these loudspeakers are often operated close to the boundary of their safe operating range.
Any electrodynamic loudspeaker is vulnerable to damage by overly large excursions of the voice coil and the cone. Typical failures are caused by the voice coil hitting the back plate or the cone suspension being torn due to excessive forward force. The loudspeakers are protected by limiting the overall amplifier power. This allows for safe operation of micro speakers with a safe distance from the boundary of the loudspeaker's safe operating area.